Reconfigurable MIMO radar

ABSTRACT

Automotive radar systems may employ a reconfigurable connection of antennas to radar transmitters and/or receivers. An illustrative embodiment of an automotive radar system includes: a radar transmitter; a radar receiver; and a digital signal processor coupled to the radar receiver to detect reflections of a signal transmitted by the radar transmitter and to derive signal measurements therefrom. At least one of the radar transmitter and the radar receiver are switchable to provide the digital signal processor with signals from each of multiple combinations of transmit antenna and receive antenna.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Provisional U.S. application62/684,982, titled “Reconfigurable MIMO Radar” and filed 2018 Jun. 14 byinventors Danny Elad, Ofer Markish, and Benny Sheinman. This provisionalis hereby incorporated herein by reference.

BACKGROUND

In the quest for ever-safer and more convenient transportation options,many car manufacturers are developing self-driving cars which require animpressive number and variety of sensors, often including arrays ofacoustic and/or electromagnetic sensors to monitor the distance betweenthe car and any nearby persons, pets, vehicles, or obstacles. Among thecontemplated sensing technologies are multi-input, multi-output radarsystems, though it can be cost-prohibitive to provide a sufficientnumber of transmitters and receivers for an adequately-performingantenna array. The prior art fails to offer a satisfactory solution tothis dilemma.

SUMMARY

Accordingly, there are disclosed herein automotive radar systems andmethods employing a reconfigurable connection of antennas to radartransmitters and/or receivers. An illustrative embodiment of anautomotive radar system includes: a radar transmitter; a radar receiver;and a digital signal processor coupled to the radar receiver to detectreflections of a signal transmitted by the radar transmitter and toderive signal measurements therefrom. At least one of the radartransmitter and the radar receiver are switchable to provide the digitalsignal processor with signals from each of multiple antennas.

An illustrative embodiment of a radar measurement method includes:transmitting a radar signal with a radar transmitter; operating a radarreceiver to provide a digital signal processor with a receive signal;processing the receive signal to detect reflections of the radar signaland to derive signal measurements therefrom; and switching at least oneof the radar transmitter and radar receiver to provide the digitalsignal processor a receive signal from each of multiple combinations oftransmit antenna and receive antenna.

Each of the foregoing embodiments may be employed individually orconjointly, and (as reflected by the claims) they may further employ oneor more of the following optional features in any suitablecombination: 1. at least some switching of the radar transmitter orradar receiver is performed during signal transmission by the radartransmitter. 2. the radar transmitter is switchable via a switch thatcouples an output of the radar transmitter to a selectable one of atleast two transmit antennas. 3. the radar receiver is switchable via aswitch that couples an input of a low noise amplifier to a selectableone of at least two receive antennas. 4. the radar receiver isswitchable via a switch that couples an input of a downconverter to aselectable one of at least two low noise amplifiers, each low noiseamplifier being coupled to a respective receive antenna. 5. the radarreceiver is switchable via a switch that couples an input of ananalog-to-digital converter to a selectable one of at least twodownconverters, each downconverter being coupled to a respective receiveantenna. 6. the radar receiver is switchable via gates that each blockor pass a signal from a respective receive antenna to an input of ananalog-to-digital converter. 7. the digital signal processor determinessignal measurements for each available combination of transmit antennaand receive antenna. 8. the digital signal processor applies phasedarray processing to derive an image from the signal measurements. 9. atleast one of the multiple antennas has a narrower beam width thananother of the multiple antennas. 10. the signal measurements includedistance and direction to at least one reflector. 11. the signalmeasurements include distance to each pixel of a beam-scan image.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an overhead view of an illustrative vehicle equipped withsensors.

FIG. 2 is a block diagram of an illustrative driver-assistance system.

FIG. 3 is a schematic of an illustrative fixed multi-input, multi-output(MIMO) radar system.

FIG. 4 is a schematic of an illustrative reconfigurable MIMO radarsystem.

FIG. 5 is a schematic of one reconfigurable MIMO system application.

FIG. 6 is a schematic of a second reconfigurable MIMO systemapplication.

FIGS. 7A-7D are schematics of various illustrative configurations for anantenna-switching receiver.

FIG. 8 is a block diagram of an illustrative MIMO radar transceiverchip.

It should be understood that the drawings and corresponding detaileddescription do not limit the disclosure, but on the contrary, theyprovide the foundation for understanding all modifications, equivalents,and alternatives falling within the scope of the appended claims.

DETAILED DESCRIPTION

FIG. 1 shows an illustrative vehicle 102 equipped with a set ofultrasonic parking-assist sensors 104 and a multiple-inputmultiple-output (MIMO) radar antenna array 106. The type, number, andconfiguration of sensors in the sensor arrangement for vehicles havingdriver-assist and self-driving features varies. For example, at leastsome contemplated MIMO radar arrays for autonomous vehicles include fourtransmit antennas and eight or more receive antennas arranged to scanahead of, around, and behind the vehicle. The vehicle may employ thesensor arrangement for detecting and measuring distances/directions toobjects in the various detection zones to enable the vehicle to navigatewhile avoiding other vehicles and obstacles.

FIG. 2 shows an electronic control unit (ECU) 202 coupled to the variousultrasonic sensors 204 and a radar array controller 205 as the center ofa star topology. Of course, other topologies including serial, parallel,and hierarchical (tree) topologies, are also suitable and contemplatedfor use in accordance with the principles disclosed herein. The radararray controller 205 couples to the transmit and receive antennas in theradar antenna array 106 to transmit electromagnetic waves, receivereflections, and determine a spatial relationship of the vehicle to itssurroundings. To provide automated parking assistance, the ECU 202 mayfurther connect to a set of actuators such as a turn-signal actuator208, a steering actuator 210, a braking actuator 212, and throttleactuator 214. ECU 202 may further couple to a user-interactive interface216 to accept user input and provide a display of the variousmeasurements and system status.

Using the interface, sensors, and actuators, ECU 202 may provideautomated parking, assisted parking, lane-change assistance, obstacleand blind-spot detection, autonomous driving, and other desirablefeatures. In an automobile, the various sensor measurements are acquiredby one or more electronic control units (ECU), and may be used by theECU to determine the automobile's status. The ECU may further act on thestatus and incoming information to actuate various signaling and controltransducers to adjust and maintain the automobile's operation. Among theoperations that may be provided by the ECU are various driver-assistfeatures including automatic parking, lane following, automatic braking,and self-driving.

To gather the necessary measurements, the ECU may employ a MIMO radarsystem. Radar systems operate by emitting electromagnetic waves whichtravel outward from the transmit antenna before being reflected back toa receive antenna. The reflector can be any moderately conductive objectin the path of the emitted electromagnetic waves. By measuring thetravel time of the electromagnetic waves from the transmit antenna tothe reflector and back to the receive antenna, the radar system candetermine the distance to the reflector. If multiple transmit or receiveantennas are used, or if multiple measurements are made at differentpositions, the radar system can determine the direction to the reflectorand hence track the location of the reflector relative to the vehicle.With more sophisticated processing, multiple reflectors can be tracked.At least some radar systems employ array processing to “scan” adirectional beam of electromagnetic waves and construct an image of thevehicle's surroundings. Both pulsed and continuous-wave implementationsof radar systems can be implemented, though frequency modulatedcontinuous wave radar systems are generally preferred for accuracy.

FIG. 3 shows an illustrative system having a fixed MIMO configuration,in which M transmitters are coupled to M transmit antennas toconcurrently send M transmit signals. The M signals may variouslyreflect from one or more targets to be received by N receive antennascoupled to N receivers. Each receiver may extract the amplitude andphase or travel delay associated with each of the M transmit signals,thereby enabling the system to concurrently obtain N*M measurements.Often the measurements need not be acquired concurrently, and theprocessing requirements associated with each receiver extracting Mmeasurements can be reduced via the use of time division multiplexingand/or orthogonal coding.

Regardless, fixed MIMO systems employ a respective antenna for eachtransmitter or receiver. This one-to-one correspondence between antennasand transmitters/receivers is widely believed to offer certainadvantages with respect to impedance matching and signal loss, andaccordingly it has long been the norm.

However, the named inventors recognize that the greater the number ofantennas, the greater the diversity of the system (i.e., the greater thenumber of independent measurements that the system can acquire and usefor image formation). Moreover, the diversity gain can more thancompensate for any switch losses incurred by associating multipleantennas with each transmitter or receiver, particularly in the contextof automotive radar systems having certain contemplated features such asactive reflectors.

Accordingly, FIG. 4 shows an illustrative reconfigurable MIMO radarsystem in which each transmitter can be selectively coupled to one of Mcorresponding transmit antennas, and each receiver can be selectivelycoupled to one of N corresponding receive antennas, enabling N*Mmeasurements to be obtained by fewer transmitters and receivers, therebymaintaining measurement diversity of the system while significantlyreducing the system's size and cost. Alternatively the number oftransmitters and receivers may be maintained while increasing the numberof antennas to significantly improve the performance of the systemwithout substantially increasing the system's cost. (Radar switches andantennas can be made with less cost than radar transmitters andreceivers.) The available antennas are systematically multiplexed to theavailable transmitters and receivers to collect the full set ofmeasurements for radar imaging.

As shown in FIG. 5, the reconfigurable MIMO system can operate toimprove the spatial resolution of radar and imaging systems whilekeeping the power consumption low. Each transmitter and receiver issequentially connected to each of the available antennas, and themeasurements are digitally combined for image formation having improvedspatial resolution. The illustrated system includes a single transmitterwith a single transmit antenna and a single receiver with two selectablereceiving antennas. Selecting between the antennas is demonstrated usinga switch. Other selection methods are possible as well.

By receiving the signal from the first antenna and then switching to theother antenna, the total aperture of the receiving system, A_(tot),becomes larger than the aperture of the single antenna, A_(single).Since image resolution is inversely proportional to the antenna aperture(large aperture generates narrow beam width), after suitable postprocessing the resolution increases. In contrast, a fixed MIMO systemwould require 2 receivers to be connected to the two receiving antennasin order to achieve the same resolution. Therefore, the reconfigurableMIMO approach provides increased resolution while keeping the powerconsumption low. In addition, since only a single receiver is used, thesize of the chip that usually used to implement the receiver can besmaller and the system cost can be reduced.

As shown in FIG. 6, the reconfigurable MIMO system can operate toimprove the range detection capabilities. To cover different detectionranges, the transmitters can be switched between transmit antennashaving narrow and wide beam widths, and the receivers can be similarlyswitched between antennas having narrow and wide beam widths. The widebeam width antennas offer a wide field of view with better sensitivityto nearby targets but lack the range to detect distant targets.Conversely, narrow bandwidth antennas offer greater range for detectingdistant targets but with their narrow field of view they may fail todetect nearby targets. The reconfigurable MIMO system may switch betweenthe antennas systematically or as needed, thereby obtaining improvedrange detection capabilities beyond what would otherwise be currentlyfeasible.

The illustrated system includes a single transmitter with two differenttransmitting antennas and a single receiver with two different receivingantennas. Selecting between the antennas is demonstrated using a switch.Other selection methods are possible as well. A more detailedexplanation on potential switching techniques is provided below. Fordetection of distant targets (Long Range Radar, useful when traveling athigh speed) a high gain and narrow beam width antenna is chosen. Fordetection of close targets (Short Range Radar, useful when travelingslowly through a crowded environment) a low gain and wide beam widthantenna is chosen. A fixed MIMO solution requires 2 transmitters and 2receivers to achieve the same dual-range capabilities. Therefore, thereconfigurable MIMO approach improves the imaging radar rangecapabilities while reducing the number of transmitters and receivers.

The proposed reconfigurable MIMO system approach connects severalantennas to each transmitter or receiver using, e.g., a switch. Thevarious new transmit-receive antenna combinations created by using theadditional antennas can, with suitable digital processing, improve theperformance of imaging radar systems. Among other things, better spatialresolution, better range detection capabilities, and better powerconsumption can be achieved compared to existing radar solutions, andthe principles disclosed herein may also be applicable to wirelesscommunication systems (e.g., 5G). In the case of communications, themain purpose of the reconfigurable MIMO is to improve the communicationcapacity in multipath environments. In the case of radar systems, thereconfigurable MIMO approach can also provide improved performance inmultipath environments, but perhaps more importantly it can improveangular resolution, multi-target tracking, and potentially providemultiple modes for increasing the detection range.

FIGS. 7A-7D show various illustrative antenna selection techniques.Though the selection techniques are illustrated for the receiveantennas, they can be similarly implemented on the transmitter side aswell.

FIG. 7A shows a receiver 702 selectively coupling one of multiplereceiver antennas 302 to an analog-to-digital converter (ADC) 704. Thereceiver 702 includes a separate connection terminal for each receiveantenna 302, and a switch 705 that selectively couples one of theterminals to a low noise amplifier (LNA) 706. LNA 706 amplifies thereceive signal from the selected antenna to improve the received signalstrength, but it is not mandatory. The output of LNA 706 is coupled to amixer 708, which multiplies the amplified receive signal with areference signal to convert the amplified receive signal to baseband.The reference signal may be, e.g., a carrier signal, afrequency-modulated carrier signal, or a buffered version of thetransmit signal. The mixer 708 and/or ADC 704 include filters to blockharmonics from the down-conversion process. ADC 704 digitizes thebaseband signal for further digital signal processing, which determinesdistance and direction information for the reflectors producing thereceive signal.

Switch 705 may be, e.g., a mechanical switch or a switch implementedusing transistors that convey weak high frequency signals with minimalattenuation or distortion. The design of FIG. 7A imposes stringentperformance requirements on the switch. FIG. 7B shows a receiver 712that somewhat relaxes the performance requirements for switch 705. Inthe design of receiver 712, each antenna connection terminal is providedwith a respective LNA 706A, 706B. Switch 705 is placed downstream of theLNAs to select between the amplified signals they produce. The switchprovides the selected signal to the input of mixer 708.

While the design of receiver 712 enables the switch 705 to work withstronger signals, there remains a requirement for good high frequencyperformance. FIG. 7C shows a receiver 722 that further relaxes theperformance requirements of switch 705. As with receiver 712, receiver722 includes a respective LNA 706A, 706B for each antenna connectionterminal. Receiver 722 further includes a respective mixer 708A, 708B todown-convert the amplified receive signals from each LNA. Switch 705selects between the baseband receive signals produced by the mixers708A, 708B. Because the spectrum of the baseband signals excludes highfrequency content, a traditional transistor-based switch or multiplexercan be employed to implement switch 705.

FIG. 7D shows a receiver 732 which combines certain features ofreceivers 712 and 722. Receiver 732 includes respective mixers 708A,708B for down-converting the receive signals from different antennas,but rather than having a switch 705 downstream of the mixers, receiver732 has a gate 733 to selectively block or pass an amplified receivesignal from LNA 706A to mixer 708A, and a second gate 734 to selectivelyblock or pass an amplified receive signal from LNA 706B to mixer 708B.The gates 733, 734 are operated in a complementary fashion such that nomore than one at a time passes an amplified signal onward.

FIG. 8 shows a block diagram of an illustrative transceiver chip 802 fora reconfigurable MIMO system. It includes 4 receivers (RX-1 throughRX-4) each of which is selectably coupled to two receive antennas 302,providing a reconfigurable MIMO system with 8 receive antennas, four ofwhich can be employed concurrently to collect measurements. Four ADCs704A-704D sample and digitize the baseband receive signals from thereceivers RX-1 through RX-4, supplying the digitized signals to adigital signal processor (DSP) for filtering and processing, or directlyto a high-bandwidth interface 804 to enable off-chip processing of thedigitized baseband signals. If used, the DSP generates image data thatcan be conveyed to an ECU via the high-bandwidth interface 804.

A control interface 805 enables the ECU or other host processor toconfigure the operation of the transceiver chip 802, including the testand calibration circuitry 806 and the transmit signal generationcircuitry 807. Circuitry 807 generates a carrier signal within aprogrammable frequency band, with a programmable chirp rate and range.Splitters and phase shifters enable the multiple transmitters TX-1through TX-4 to operate concurrently if desired. In the illustratedexample, the transceiver chip 802 includes 4 transmitters (TX-1 throughTX-4) each of which is fixedly coupled to a corresponding transmitantenna 301. In alternative embodiments, multiple transmit antennas areselectably coupled to each of the transmitters.

A potential disadvantage of employing a reconfigurable MIMO system withmultiple receive antennas is the time required to repeat measurementswith different combinations of transmit and receive antennas. In certaincontemplated embodiments, the time required may be minimized byperforming antenna switching during ongoing signal transmission. Forexample, while a transmitter is sending a transmit signal from aselected antenna, each receiver may acquire a first measurement with afirst selected antenna and then, while the pulse transmission continues,switch to a second selected antenna to collect a second measurement.Additionally, or alternatively, while the transmitter is sending atransmit pulse via a first selected antenna, the transmitter may switchto a second selected antenna, enabling each receiver to obtainmeasurements responsive to the use of each transmit antenna.

Though the operations described herein may be set forth sequentially forexplanatory purposes, in practice the method may be carried out bymultiple components operating concurrently and perhaps evenspeculatively to enable out-of-order operations. The sequentialdiscussion is not meant to be limiting. Moreover, the focus of theforegoing discussions has been radar sensors, but the principles areapplicable to any MIMO transducer array systems. These and numerousother modifications, equivalents, and alternatives, will become apparentto those skilled in the art once the above disclosure is fullyappreciated. It is intended that the following claims be interpreted toembrace all such modifications, equivalents, and alternatives whereapplicable.

What is claimed is:
 1. An automotive radar system that comprises: aradar transmitter; a radar receiver; and a digital signal processorcoupled to the radar receiver to detect reflections of a signaltransmitted by the radar transmitter and to derive signal measurementstherefrom, wherein at least one of the radar transmitter and the radarreceiver are switchable to provide the digital signal processor withsignals from each of multiple selectable antennas, and wherein at leastone of the multiple selectable antennas has a narrower beam width thananother of the multiple selectable antennas.
 2. The automotive radarsystem of claim 1, wherein at least some switching of the radartransmitter or radar receiver is performed during signal transmission bythe radar transmitter to split transmission or reception of a transmitpulse across multiple antennas.
 3. The automotive radar system of claim1, wherein the radar transmitter is switchable via a switch that couplesan output of the radar transmitter to a selectable one of at least twotransmit antennas.
 4. The automotive radar system of claim 1, whereinthe radar receiver is switchable via a switch that couples an input of alow noise amplifier to a selectable one of at least two receiveantennas.
 5. The automotive radar system of claim 1, wherein the radarreceiver is switchable via a switch that couples an input of adownconverter to a selectable one of at least two low noise amplifiers,each low noise amplifier being coupled to a respective receive antenna.6. The automotive radar system of claim 1, wherein the radar receiver isswitchable via a switch that couples an input of an analog-to-digitalconverter to a selectable one of at least two downconverters, eachdownconverter being coupled to a respective receive antenna.
 7. Anautomotive radar system that comprises: a radar transmitter; a radarreceiver; and a digital signal processor coupled to the radar receiverto detect reflections of a signal transmitted by the radar transmitterand to derive signal measurements therefrom, wherein at least one of theradar transmitter and the radar receiver are switchable to provide thedigital signal processor with signals from each of multiple antennas,wherein at least one of the multiple antennas has a narrower beam widththan another of the multiple antennas, wherein the radar transmitter isswitchable via a switch that couples an output of the radar transmitterto a selectable one of at least two transmit antennas, and wherein theradar receiver includes a downconverter for each receive antenna, thedownconverters each having an output coupled to a given input of ananalog to digital converter, wherein the radar receiver is switchablevia gates that each block or pass a signal from a respective receiveantenna to an input of a respective one of the downconverters.
 8. Theautomotive radar system of claim 3, wherein the digital signal processordetermines signal measurements for each available combination oftransmit antenna and receive antenna.
 9. The automotive radar system ofclaim 3, wherein the digital signal processor applies phased arrayprocessing to derive an image from the signal measurements.
 10. A radarmeasurement method that comprises: transmitting a radar signal with aradar transmitter; operating a radar receiver to provide a digitalsignal processor with a receive signal; processing the receive signal todetect reflections of the radar signal and to derive signal measurementstherefrom; and switching at least one of the radar transmitter and radarreceiver to provide the digital signal processor a receive signal fromeach of multiple combinations of transmit antenna and receive antenna,wherein a receive antenna in at least one of the multiple combinationshas a narrower beam width than a receive antenna in another of themultiple combinations.
 11. The radar measurement method of claim 10,wherein at least some switching of the radar transmitter or radarreceiver is performed during signal transmission by the radartransmitter to split transmission or reception of a transmit pulseacross multiple antennas.
 12. The radar measurement method of claim 10,wherein the radar transmitter is switchable via a switch that couples anoutput of the radar transmitter to a selectable one of at least twotransmit antennas.
 13. The radar measurement method of claim 10, whereinthe radar receiver is switchable via a switch that couples an input of alow noise amplifier to a selectable one of at least two receiveantennas.
 14. The radar measurement method of claim 10: wherein theradar receiver is switchable via a switch that couples an input of adownconverter to a selectable one of at least two low noise amplifiers,each low noise amplifier being coupled to a respective receive antenna.15. The radar measurement method of claim 10, wherein the radar receiveris switchable via a switch that couples an input of an analog-to-digitalconverter to a selectable one of at least two downconverters, eachdownconverter being coupled to a respective receive antenna.
 16. A radarmeasurement method that comprises: transmitting a radar signal with aradar transmitter; operating a radar receiver to provide a digitalsignal processor with a receive signal; processing the receive signal todetect reflections of the radar signal and to derive signal measurementstherefrom; and switching at least one of the radar transmitter and radarreceiver to provide the digital signal processor a receive signal fromeach of multiple combinations of transmit antenna and receive antenna,wherein at least one of the multiple antennas has a narrower beam widththan another of the multiple antennas, wherein the radar transmitter isswitchable via a switch that couples an output of the radar transmitterto a selectable one of at least two transmit antennas, and wherein theradar receiver includes a downconverter for each receive antenna, thedownconverters each having an output coupled to a given input of ananalog to digital converter, wherein the radar receiver is switchablevia gates that each block or pass a signal from a respective receiveantenna to an input of a respective one of the downconverters.
 17. Theradar measurement method of claim 10, wherein the digital signalprocessor determines signal measurements for each available combinationof transmit antenna and receive antenna.
 18. The radar measurementmethod of claim 10, wherein the digital signal processor applies phasedarray processing to derive an image from the signal measurements.